1. Field of the Invention
The present invention relates to mass spectrometers and, more particularly, single focusing mass spectrometers.
The first single focusing mass spectrometer was built by Dempster and then ion optic systems with the first order approximation were completed by Herzog. Such ion optic systems are now widely used in the mass spectrometers. The instruments now put into practical application generally comprise a 60.degree. or 90.degree. sector type, homogeneous magnetic field with normal incident and exit angles. Some attempts have been made to improve performance of the instruments on the basis of ion optical considerations. For example, Kerwin had proposed to introduce a wide-angle focusing system into the mass spectrometers. However, none of the proposals have ever been put into practical application because of the following reasons. In the proposed ion optical systems, the ion trajectories were determined on the orbit plane without taking the influence of the magnetic fringing fields into consideration. However, the magnetic field distribution differs at the fringing field out of the orbit plane even in the homogeneous magnetic field. This results in the deviation of ion trajectories, which causes aberration. For this reason, it is impossible to produce mass spectrometers with high performance using this approach.
Recently, a trajectory calculation method has been developed for determining the trajectories of ions passing through the magnetic fringing field, with accuracy to the third order approximation, making it possible to calculate second and third order aberrations in any ion optic system. Using this method, the ion optic systems in the conventional instruments were investigated. The results showed that these single-focusing mass spectrometers have aberration problems awaiting solution.
It is an object of the present invention to provide a single-focusing mass spectrometer with low aberration coefficients and a high resolving power.
Another object of the present invention is to provide a small-sized single-focusing mass spectrometer.
Still another object of the present invention is to provide an ion optical system for single-focusing mass spectrometers that makes it possible to obtain high resolving power and small aberrations and to construct small-sized mass spectrometers with these features.
According to the present invention there is provided a mass spectrometer comprising a source for generating ions, a means for separating the ions according to mass, and means for detecting the separated ions, characterized in that said means for separating ions comprises a sector type homogeneous magnetic field with a deflection angle ranging from 110 to 135 degrees, and incident and exit angles ranging from 40 to 60 degrees from the normal.
The invention will be further apparent from the following description taken in conjunction with the accompanying drawings.